The present invention relates to a ratchet mechanism which is particularly useful in pushbutton switches for use in electrical circuits and in particular to pushbutton switches where it is desired that action be xe2x80x9csoftxe2x80x9d, both in sound and tactile feel. In one embodiment this may be a momentary ON switch in which electrical contact is made upon advancing the plunger and contact is broken when the plunger retracts.
A pushbutton switch as described and illustrated in U.S. Pat. No. 6,191,376 is a convenient means for describing the improvements that make the ratchet mechanism used in this switch much quieter and smoother. The subject matter of U.S. Pat. No. 6,191,376 is hereby incorporated by reference. The ratchet mechanism is useful in other pushbutton switches and in other applications where a reciprocating motion is converted to stepwise rotary motion. Such an application is in some ball point pens, for example, where pressing the plunger on the pen advances the writing tip and also rotates the cartridge with the writing tip to distribute wear on the ball.
There has been continued interest in making switches quieter and although some designs have been successful, further improvement is desirable. Some approaches have resulted in adding parts to a switch with consequent cost increase. An example is in U.S. Pat. No. 4,939,328. Better solutions to quieting a switch are desirable.
In a presently preferred embodiment (exemplified in the description and drawings in a switch), the ratchet mechanism has a plunger having at least one longitudinally extending tooth and constrained to translational motion cooperating with a ratchet member having a plurality of longitudinally extending teeth for engaging a tooth on the plunger and movable both in translation and in rotation. Each tooth on the plunger has a driving face at an angle from a plane normal to the longitudinal direction of the plunger wherein the angle is close to the sum of the arctangent of the coefficient of friction between the ratchet teeth and the plunger tooth and the arctangent of the effective coefficient of friction of other sliding surfaces.
In an exemplary embodiment in a pushbutton switch, there is a body including a barrel and a plunger longitudinally movable in the barrel. A ratchet including a plurality of longitudinally extending camming teeth is coaxial with the plunger. There are a plurality of longitudinally extending camming teeth on the plunger for engagement with camming teeth on the ratchet (one tooth on the plunger being sufficient), each plunger tooth including a driving face having an angle from a normal to the longitudinal direction of the plunger wherein the angle is in the range of from the arctangent of the coefficient of friction between the ratchet teeth and the plunger tooth plus the arctangent of the effective coefficient of friction between other parts moved by depressing the plunger, up to about 30 degrees.